Assessing Acidity Qualitatively - All Four Factors - Exercise 25

Exercise 3.25 - Assessing Acidity Qualitatively - All Four Factors

Introduction

This video covers Exercise 3.25, focusing on qualitatively assessing the acidity of different compounds using four main factors: Atom, Resonance, Induction, and Orbitals (REO). These factors help determine which hydrogen atoms in a molecule are more acidic.

Main Points

• Atom:

- Compare the atoms bonded to the hydrogen.

- In a row on the periodic table, the hydrogen on the atom further to the right is more acidic.

- In a column, the hydrogen on the atom lower down is more acidic.

• Resonance:

- Determine if the removal of a hydrogen atom creates a lone pair that can participate in resonance.

- The more resonance structures a molecule can form, the more stable the conjugate base, and thus the more acidic the hydrogen.

• Induction:

- Evaluate the presence of electronegative atoms near the acidic hydrogen.

- Electronegative atoms pull electron density through sigma bonds, stabilizing the negative charge and increasing acidity.

• Orbitals:

- Consider the hybridization of the atom bonded to the hydrogen.

- The more s-character in the orbital (e.g., sp > sp2 > sp3), the more acidic the hydrogen.

Examples/Evidence

• Example A:

- Red hydrogen on oxygen, blue hydrogen on carbon.

- Atom factor: Oxygen is more electronegative than carbon, making the red hydrogen more acidic.

• Example B:

- Both hydrogens on carbon, but different resonance possibilities.

- Red hydrogen leaves a lone pair involved in more resonance structures, making it more acidic.

• Example C:

- Red hydrogen on oxygen, blue hydrogen on nitrogen.

- Atom factor: Oxygen is further to the right than nitrogen, making the red hydrogen more acidic.

• Example D:

- Both hydrogens on carbon, different resonance involvement.

- Blue hydrogen's lone pair is involved in more resonance, making it more acidic.

• Example E:

- Red hydrogen on nitrogen, blue hydrogen on carbon.

- Atom factor: Nitrogen is further to the right than carbon, making the red hydrogen more acidic.

• Example F:

- Red hydrogen on oxygen, blue hydrogen on sulfur.

- Atom factor: Sulfur is lower in the column than oxygen, making the blue hydrogen more acidic.

• Example G:

- Red hydrogen on carbon, blue hydrogen on nitrogen.

- Atom factor: Nitrogen is further to the right than carbon, making the blue hydrogen more acidic.

• Example H:

- Both hydrogens on oxygen, different resonance involvement.

- Blue hydrogen is closer to an electronegative atom, making it more acidic.

• Example I:

- Red hydrogen on nitrogen, blue hydrogen on oxygen.

- Atom factor: Oxygen is further to the right than nitrogen, making the blue hydrogen more acidic.

Conclusion

The video demonstrates how to use the REO factors to assess the relative acidity of different hydrogens in a molecule. By considering the atom, resonance, induction, and orbitals, one can determine which hydrogen is more acidic.